Gas burners for domestic use, in particular if designed to deliver a high thermal power, can suffer from the phenomenon of backfire, i.e. the fact that when the burner is turned off, therefore interrupting the flow of combustion gas into the Venturi effect mixer, the flame present outside the flame spreader can enter the burner and spread to the gas-primary air combustion mixture which is still present, stationary, inside the burner during the moments immediately after turn-off.
In particular, in the case of immediate re-ignition after the burner has been turned off, even 3-4 seconds after turn-off, the phenomenon of backfire, due in this case to the presence of unburned mixture inside the burner, ignited by the new flame lit by the user, is particularly frequent.
This phenomenon, which occurs in particular with the use of mains gas (“town gas”, G110-8 mbar) as combustible gas, can be extremely harmful for some of the burner internal components, such as the Venturi effect mixer and, above all, the combustion gas injector, which is usually made of a material not able to effectively withstand the temperatures of the flame.
To prevent this phenomenon, in the known art a flat wire net is provided, having a fine mesh (for example 1 mm2), which is positioned immediately downstream of the flame spreader and has the function of splitting the fluid flow into various fluid streams, imposing a local acceleration of said fluid flow when it crosses the above-mentioned wire net meshes, which is sufficient to stop the flame from spreading beyond said wire net.
For example, GB-A-1100278, in the name of Societe Anonyme La Couvinoise, teaches how to position, in a gas burner, a flat wire net inside the combustion mixture distribution chamber, immediately upstream of the relative flame spreader. Said wire net, obviously having a fine mesh, is able to arrest any propagation of the flame inside the above-mentioned burner distribution chamber and therefore inside the Venturi effect mixer, through to the relative injector.
While being effective in countering the phenomenon of backfire during turn-off of the burner, this solution nevertheless has some drawbacks, including the fact that it is necessary to provide a wire net with shape and dimensions such as to adapt perfectly to the geometry of the above-mentioned burner chamber, and the fact that said wire net, positioned near the holes of the flame spreader inside the mixture distribution chamber, can constitute an obstacle to correct distribution of the combustion mixture to the relative flame spreader, with consequent possible anomalies in distribution of the burner flames.
Furthermore, in the case of use of the burner described by GB-A-1100278 as a domestic burner for cooking food, arrangement of the wire net near the holes of the flame spreader entails on the one hand the risk of the user forgetting to refit the wire net after cleaning the burner, even superficially, and, on the other, the risk of remains of food getting into said wire net, with probable obstruction of at least part of the mesh and consequent malfunctioning of the burner.
The object of the present invention is therefore to provide a domestic gas burner comprising at least one Venturi effect mixer in fluid connection with at least one combustion mixture distribution chamber and with a relative flame spreader, which is provided with means for preventing propagation of the flame by splitting the fluid flow, without the drawbacks of those used in the known prior art.
A further object of the present invention is to provide a gas burner that effectively stops any backfire from penetrating into the burner structure, while being simple and inexpensive to produce.
A further object of the present invention is to produce a gas burner which comprises means for preventing propagation of the flame within said burner which are simple to produce, do not cause malfunctioning of the burner and at the same time are easy to assemble and disassemble inside the burner, while preventing accidental incorrect assembly.
A further object of the present invention is to produce a gas burner with means for preventing propagation of the backfire (i.e. back flames) able to prevent propagation of the backfire generated both during turn-off of the burner and during the turn-on transient.